1. Technical Field
The present invention relates to a laser light source.
2. Related Art
As light sources that emit laser light, laser light sources that emit light having a narrow spectrum line-width are required.
The line-width of laser light is inversely proportional to the square of a resonator length when a loss of a waveguide constituting an optical resonator is sufficient small. On the other hand, the line-width is inversely proportional to the resonator length when the waveguide loss is large.
Electronics Letters, vol. 21, No. 3, pp 113-115, 1985 discloses that the contraction of a spectrum line-width is achieved by increasing the length of an optical resonator.
However, the inventor has found the following various problems. When the length of the optical resonator is increased, adjacent longitudinal mode light having high intensities is generated. When multiple-stage optical filters are provided within the optical resonator in order to prevent the adjacent longitudinal mode light from being output, the waveguide loss of the optical resonator increases, and a contraction effect of the line-width due to an increase in its length is reduced.
Japanese Unexamined Patent Publication No. 2012-33807 discloses that a reduction in line-width is performed without increasing a resonator length by adjusting the amount of detuning of the optical filter which is inserted into the optical resonator, but the structure of the optical resonator becomes complicated.
An object of the present invention is to provide a laser light source that outputs light having a narrow spectrum line-width using an optical resonator of a simple structure.